Method of forging magnesium



July 7, 1936. R W OD 2,046,355

METHOD OF FORGI NG MAGNESIUM Filed NOV. 17, 1932 INVENTOR Patented July 7, 1936 UNITED STATES METHOD or FORGING MAGNESIUM- Robert T. Wood, Cleveland, Ohio, assignor, by mesne assignments, to Magnesium Development Corporation, a corporation of Delaware Application November 17, 1932, Serial No. 643,032

5 Claims. (Cl. 78-12) The invention relates to a method of forging magnesium and its alloys, with particular reference to reducing the cross sectional area of billets and rectangular bars in order to produce bars of smaller cross section.

Magnesium is unlike aluminum and steel in that it cannot be successfully drawn into bar or rod by the simple expedient of subjecting the billet to the forging action of a set of flat dies, With this method as applied to either steel or aluminum, the billet is drawn, i. e. passed between a set of forging dies, then rotated through an angle of 90 degrees and again passed through the same set of dies, the hammering action of the dies serving to elongate the billet as its cross sectional area is reduced. When, however, a magnesium billet is forged in this manner, it does not elongate very much, but tends to spread laterally about as much as in the longitudinal direction. This results in severe shear stresses along planes disposed at an angle of approximately 45 degrees with respect to the die faces. The metal slides back and forth along these shear planes until the bar cracks and the end bursts open.

It is an object of my invention to devise a method for forging bars of magnesium and its alloys which overcomes the difliculty aforementioned and makes it possible to increase the extent to which a billet of magnesium can be reduced in cross sectional area without the production of serious cracks or other defects. It is a further object of the invention to provide a method and apparatus for the purpose described which will serve to increase the longitudinal plastic flow of the metal and thus fioduce a sounder bar through elimination of the severe shear stresseswhich are occasioned when it is attempted to forge magnesium with the usual apparatus and according to the usual methods used in working steel or in working aluminum.

I have found that if the working face of one or both of the forging dies is made partially cylindrical in form, the longitudinal flow of metal is increased suificiently to prevent shear cracking and bursting. As an example whereby my invention may be understood and practiced by those who are familiar with this art, reference is made to the accompanying drawing illustrative of a preferred embodiment.

In the drawing Fig. 1 shows in diagrammatic perspective view a pair of dies embodying the features of my improved apparatus; Fig 2 is a perspective view of a magnesium billet which is to be reduced; Fig. 3 is a perspective view of the same billet after it has been partially drawn through the dies; Fig. 4 is a perspective view of the billet at a later stage of the forging operation; Fig. 5 is a perspective view of the finished bar; and Fig. 6 is a longitudinal cross sectional 5 view of a die similar to those illustrated in Fig. 1, but showing a somewhat modified construction. Fig. 7 is a perspective view of a billet which has been partially reduced according to a slightly modified sequence of forging steps.

Referring particularly to Fig. 1, there is shown a pair of forging dies comprising the upper and lower die members I and 2 respectively. The die members I and 2 may be mounted in any convenient manner well known to those familiar with the construction and operation of forging hammers. Thus the member 2 may be secured to the anvil of the hammer and the member I may be secured by the usual means to the tup. The essential feature of a forging die constructed in accordance with the present invention is the provision of the centrally located raised portion 3. This raised portion 3 is cylindrical or partly cylindrical in form; that is to say, it may correspond to a portion of the surface of a right circular cylinder or of a cylinder other than a right circular cylinder. It is tobe distinctly understood that throughout the specification and in the claims the term cylinder (and its derivatives) is used in its generic geometrical signification and not in the sense in which it is loosely employed as denotng that special form of cylinder which is properly described as a circular cylinder. For example, a right cross section of the raised portion 3 of my improved die may be a partial ellipse instead of a circular arc. Again, it may be partly curved and partly fiat as will appear further on in connection with a description of another embodiment. At each side of the raised central portion 3 there may be a flat por- 40 tion 4 which serves as a base or mounting for the raised or working portion 3 of the die.

If desired the die as just described may be combined with an ordinary fiat die as shown in Fig. 1 by providing an adjacent flat working surface 5 which is used for producing a smooth surface on the finished bar.

It will be understood that while I have shown a unitary die construction embodying both the special cylindrical working surface and the ordinary fiat working surface, it would be prac-' ticable to sepaarte thetwo portions of the die and mount them in separate hammers. As a matter of practical convenience, however, I prefer to embody the two in a unitary structure as shown. The uneven surface produced by the cylindrical dies may be smoothed down by other means than fiat dies suggested, as by means of rolls or otherwise.

Referring now to Fig. 2, the billet is conveniently provided with a tong hold I by hammering down one end of the billet in a well known manner. The end of the billet is then grasped with the tongs and it is passed between the die members I and 2, which hammer it down as it passes therebetween in a manner indicated in Fig. 3, which shows the form of the billet after the first pass has been partially completed.

The direction of movement of the billet 6 between the dies is indicated by the dotted line A-B in Fig. 1. For purposes of definition this may be described as a direction normal to a plane containing an element of the cylindrical surface as oontradistinguished from a direction parallel to such a plane.

The result of the first step which has been described is to elongate the billet in a longitudinal direction without increasing the width to any extent. The portion of the billet which has been subjected to the hammering action of the dies is indicated at 8. The surface will be somewhat irregular or scalloped because of the'form of the working surface of the dies, but this irregularity can be removed at any time during the reduction of the billet by shifting it to the side of the die which has the fiat surface 5. When this is done, the blows of the hammer are preferably lightened so as to obviate the production of undesirable shear stresses.

Fig. 4 shows a further step in the reduction the billet having been turned through an angle of degrees around its longitudinal axis after the completion of the pass indicated in Fig. 3. Fig. 5 shows the completed bar, the surfaces of which have been smoothed off by lightly hammering between the fiat portions 5 of the dies.

Fig. 6 illustrates another embodiment in which theraised portion 9 of the die is provided with a fiat upper surface l0 and rounded corners II. The working. surface of this die which comprises the flat portion I0 and the rounded portions Ii may be described as cylindrical in form within the meaning of that term as employed herein and in the appended claims.

It will be understood that, instead of passing the billet completely through the dies without rotating through an angle of 90 degrees, and

then, after such a rotation, again passing the billet completely through the dies, the billet may be rotated through an angle of 90 degrees after each successive hammer blow, giving an appearance such as is shown in' Fig. 7.

The advantages obtained by using this form of forging die have been conclusively demonstrated in the tests which I have performed. I have found, for example, that when it is attempted to draw a bar 2% inches by 2% inches in section from a magnesium allow ingot containing small amounts of manganese and tin, using regular fiat dies, the bar cannot be reduced under 3 /2 inches by 3 inches in section without cracking. By reducing the 8 inch by 8 inch ingot to 6 inches by 6 inches between flat dies and then using a pair of dies constructed in accordance with the present invention, a bar 2%, inches by 2 4- inches in section was produced without difficulty, the bar showing no evidence of shear cracking.

Of course it is to be understood that the design of the die may vary with the size of the die, but this is a matter which can readily be 10 determined by experiment for any given case. Furthermore, it is not necessary that the entire reduction be performed by means of my improved dies, as it will frequently be found possible to perform I preliminary or intermediate steps in the reduction by means of regular flat dies. Again, as has been noted, the flat dies may be used to produce a smooth surface in the finished bar. The invention in its broadest aspects, therefore, contemplates the utilization of 20 the special form of die during any substantial portion of the reducing operation.

I further contemplate the use of a die provided with a cylindrical working surface in conjunction with a flat die. It will be apparent that 25 with two dies of the form shown in Figs. 1 or 6, the longitudinal flow of the metal would be en- 'couraged to a greater width than when one of the convex dies is opposed to a flat die. Yet the latter arrangement represents an improvement 30 over the use of two flat dies, and accordingly the advantages accruing from the invention will be realized to a' certain extent and this combination of a flat die and a convex die may even be preferable in some cases. 35

In the interest of clarity, I have described my invention -.with reference to specific embodiments and have employed specific language, but it is to be understood that I have no intention of excluding such mechanical equivalents as may fall within the terms of the claims.

I claim:

1. The method of forging bars of magnesium and its alloys which comprises subjecting a magnesium billet to the transverse hammering action of dies, one of which has at least a portion of its working surface of convexly-curved cylindrical form, drawing the billet through the dies in a direction normal to a plane containing an element of the cylindrical surface, and turning the billet through an angle of 90 degrees between successive passes through the dies.

2. The method of forging bars of magnesium and its alloys which comprises subjecting a magnesium billet to the transverse hammering action of a pair of dies, each of which has a working surface which is at least partly raised in cylindrical form, drawing the billet through the dies in a direction normal to a plane containing an element of the, cylindrical surface, and tuming the billet through an angle of 90 degrees between successive reductions.

3. The method of forging bars of magnesium and its alloys which comprises subjecting a magnesium billet to the transverse action of dies, one of which has at least a portion of its working surface raised in cylindrical form, drawing the billet through the dies in a direction normal to a plane containing an element of the cylindrical surface, and turning the billet through 70 an anglev of 90 degrees between each successive hammer blow. v

4. The method of forging'bars of magnesium and its alloys which comprises subjecting a magnesium billet to the transverse hammering action 76 of dies, each of which has a working surface which is at least partly raised in cylindrical form, to transversely groove the billet, drawing the billet through the dies in a direction normal to a plane containing an element of the cylindrical surface, and turning the billet through an angle of 90 degrees between successive passes through the dies.

5. The method of forging bars of magnesium and its alloys which comprises subjecting a magnesium billet to the transverse action of dies,

one of which has at least a portion of its working surface of convexly curved cylindrical form, to produce continue-us transverse ooves across the width of the billet, drawing the billet through the dies in a direction normal to a plane containing an element of the cylindrical surface, and turning the billet through an angle of 90 degrees between each successive hammer blow.

ROBERT T. WOOD. 

